My Fitbit Charge HR broke. I was just sent a new one. can I sync it with my existing app?

Which model?
You can get replacements here:

Fitbit Store Buy Surge Charge HR Charge Flex One Zip Aria

When your Fitbit isn't syncing or your device unpretentiously isn't turning on, letting all your fitness data go unauthorize is disappointing. While we love Fitbits, they're as apt to device issues as any other gadget. So, if you're intensely googling "How toReset Fitbit Charge HR" or "Fitbit charge HR not syncing" then you are at the right place. We are going to cover more than your expectation. The process of Reset Fitbit Charge HR is very easy.
Here, we are going to analyze what to do if your device isn't working properly - and when you need to perform a full factory reset.

Of course you can do it with a screen protector.
The Guide Of Reset Fitbit Charge HR Complete Guide

go into the app and make sure you have selected steps to show on your fitbit.

How to fix broken Fitbit - sync Fitbit with phone app - PC ...

www.pcadvisor.co.uk/how.../how-fix-broken-fitbit-sync-image-3499292...

May 15, 2015 - Fitbit Flex, Fitbit One, Fitbit Zip, Fitbit Force or Ultra not syncing with the Fitbit app ... To get the Fitbit app sync working again restart the Fitbit tracker. ... charger, has a battery charge but is not lighting up, or isn't tracking your steps. .... I've already done all the obvious stuff: turning off my phone, turning off and ...

Fitbit Flex review - The disappointment we've all been ...

blog.hyperexpert.com/fitbit-flex-review-the-disappointment-weve-all-be...

May 5, 2013 - My wife and I are both in good shape, we both wanted the Flex just to ... app, wait for the device to finish connecting and syncing to your phone, ... to sleep mode, I have to do all of this? and then again to wake it up? .... Also, doesn't the manual say "not" to wear it in the shower? ..... I appreciate any response.

https://help.fitbit.com/articles/en_US/Help_article/How-do-I-restart-my-tracker
pick charge hr to see instructions on this model

Fitbit has the manuals for most of their products on their support site. For the Charge HR, see http://help.fitbit.com/?p=charge_hr . The link to the manual is the first link in the line "Charge HR Resources" near the top of the web page. The direct link is https://staticcs.fitbit.com/content/assets/help/manuals/manual_charge_hr_en_US.pdf .

I hope this helps.

Cindy Wells