How can I unlock my ZTE Z291DL mobile hotspot

SOURCE: how do i unlock the mobile hotspot feature

You have to have a 5 gigabyte data feature for $50 a month or one of our new mobile share rate plan (share group data with unlimited talk & text for up to 10 lines) in order to use your hotspot feature on your phone. You can change your data feature on your online acct or call 611 from your cell phone.

SOURCE: Can someone please unlock the AT&T Sierra Wireless Aircard 754S Mobile Hotspot

We don't unlock phone. Please goto your provider, of visit a less legal unlock site that can do the service for a fee.
Just google with the words unlock my ........ phone

SOURCE: How do I access a mobile hotspot option for my straight talk zte z963vl android version 5.1.1? My phone does not have the option in my settings for mobile hotspot and tethering..

It should be there...Goto Settings - Wireless & Network - Tethering & Portable Hotspots .
First though activate the Wifi then the Tethering option as described above.
Switch on any device you want to tether to and look for your device name (or you can setup a password from same list) and continue to tether.
Be advised though, some Network Operators will tell you that it's unable to tether or warn you against it. But I've had this a few times and I still tether what I like.
also be advised that if you on capped data plan, keep an eye on your data limits.
Good luck.