How do I get rid of iOS 26 on my iPhone?

Follow the Support Article below for instructions. You'll need to connect your iPhone to a computer and put it into Recovery Mode, allowing you to Restore with the latest public release of iOS, 18. Hopefully you had an archive of a backup on your computer or an iCloud Backup that was not overwritten which you can restore from.

How to uninstall iOS or iPadOS beta software - Apple Support

Read the documentation provided to you when joining the developers beta.

Ella_6390 wrote:

I want to get rid of the new iOS 26 beta as it’s using all my battery up

Since you're a developer, you must have known to make an Archive Backup on your computer before you downloaded the beta, right? If you didn't, you're going to lose all the data on your phone in the restore process, except things you were syncing with iCloud. Apple advises to NEVER install beta software on your primary device. Public testing won't begin for a few weeks and the actual public release won't happen until this fall. Patience is a virtue, they say!

How to remove beta -

https://beta.apple.com/sp/betaprogram/unenroll