iPhone using another apple id instead of main one

IOS updates or app updates? Are you seeing an Activation Lock?

If IOS updates, if this is a used device, the previous owner needs to log out of iCloud or go to https://www.icloud.com/find/ and erase the device, then remove it from their account. If they won't do that, the device is useless. Apple won't unlock it.

Turn off Activation Lock - Apple Support.     

If you are the original owner, contact Apple. Apple can remove the ID  if provided the required paperwork. 

Request additional support for unlocking your device

Either take the device, the original purchase receipt with the serial number, and a photo ID to the nearest Apple Store (if it has reopened). Call the store before going to make sure they can help.

Genius Bar Reservation and Apple Support Options - Apple.    

or contact Apple ID Support. 

 Apple ID - Official Apple Support.    

Contact Apple for help with Apple ID account security - Apple Support.      (Link doesn’t always load)   

Get Support   https://getsupport.apple.com        Work through the screens to get a chat option. 

Apple Support schedule phone call        

https://twitter.com/AppleSupport       

If app updates, those purchases are tied to the other ID and can't be transferred. One option is to delete the apps/purchases made by the other ID and download them using the new ID if desired. After deleting the apps, it may be necessary to restart the device/computer before you can download the apps again. If necessary, check your purchases history to see which apps/purchases weren’t made by the current ID. 

You are welcome. Check your purchases history.

Purchase History Review.  

You can try setting up Family Sharing between the IDs if you want to be able to share purchases made with the IDs.

Family Sharing.         

Family Sharing - Set up.