Adjust handle bar height ?

Yes, all bikes have handlebar height adjustment.

How to Adjust the Handle Bars on a Mongoose Mountain ...

DIY Mountain Bike https://www.diymountainbike.com > adjust-handle-bar...
This is done by loosening the bolt and clamp on the front of the stem. Insert a 6mm Allen wrench into the bolt head and turn until the handle bars roll freely.

How to Raise Handlebars on Mongoose Mountain Bike

mtbrules.com https://mtbrules.com > how-to-raise-handlebars-on-mo...
Oct 2, 2022 - You can adjust the handlebars from front to back by loosening the clamp bolt in the stem's front. Insert a 6 mm Allen wrench into the bolt head.

How to Raise the Handlebars on a Mongoose

SportsRec https://www.sportsrec.com > Fitness > Strength Training
Jun 29, 2011 - Other options for raising Mongoose handlebars are adding a new riser bar, which can give 1 to 5 inches of height for your handlebars. A steer- ...

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Product Manuals

Mongoose https://www.mongoose.com > pages > product-manuals
The Mongoose owner's manual contains important safety, performance and maintenance information. Read the manual before taking your first ride on your new ...

According to the manual:

If your bike has a "threadless" stem (fig. 6) your dealer may be able to change handlebar height by moving height adjustment spacers from below the stem to above the stem, or vice versa. Otherwise, you'll have to get a stem of different length or rise. Consult your dealer. Do not attempt to do this yourself, as it requires special knowledge.

If your bike has a "quill" stem (fig. 7) you can ask your dealer to adjust the handlebar height a bit by adjusting stem height. A quill stem has an etched or stamped mark on its shaft which designates the stem's "Minimum Insertion" or "Maximum Extension". This mark must not be visible above the headset.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiuyuupw8HZAhUEU98KHRk1BaoQFggpMAA&url=http%3A%2F%2Fkhsbicycles.com%2FPDF%2FKHS-Owners-Manual.pdf&usg=AOvVaw1LLFcErB5Fxs_LpkLUwB-K

Your bike has a modern "threadless headset" which usually allows very little vertical adjustment. See this page for an explanation of how to change height on that style:
How to adjust handlebar height BikeRadar
If you can't adjust enough that way you can try buying a shorter stem or one with a steeper angle,. The final option is to buy a "stem riser" - Google the term for more info - needs to have correct dimensions for your bike

It's best to get advice at a bike shop as to what option is best for you..

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

Robert, Below I have posted links showing how to adjust handle bar height for most, some bikes bars are not adjustable and are welded. If the links do not help I suggest you do a google search. Check the attached links,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
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Today's bike stems have minimal adjustment height, if any. Look at your stem to see if it has spacers. These spacers can be moved up and down the stem. For more adjustments, you will have to buy a new stem. Here is a good place to read up on
How to adjust handlebar height BikeRadar

There is no alternative handle / handlebar adjustment for the Quinny Zapp.

You need to loosen the neck of the handle bars with a anlenwrinch.After that you will be able to adjust the hieght of the handle bars by lifting the top of them.

Most bikes use an allen key to adjust the height of the handle bars. Typically 6mm. But be careful most bikes do not have much adjustment that can be done to the height of the handle bars. The handle bar stem will have a line on it of the "minimum insertion". That line must be below the top of the head set nut for safety reasons. Look for the line as you adjust the height.

some bikes u cant only the seats can adjuct

the handle bars run thru your neck in the center, you should find a hex head bolt inthe center of the neck, loosen it then pull the handle bars up, be careful not to unscrew the entire bolt in the neck