When ever I try to download my apps it opens someone else Apple ID login ,how can I remove it

You have apps installed that were purchased and downloaded using the old Apple ID. You either need to provide the password for that Apple ID, or identify and remove the apps that were purchased with it.

There is no easy way to identify those apps. You can try updating them one at a time in the App Store app. Any app that requires the password for a different Apple ID should be removed and repurchased with your own ID.

If you are the owner or the owner has shared all information with you then to open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.

If you are not the owner and do not have the Apple ID and Password then there is no way that you can get into this iPhone unless the original owner shares the Apple ID and password with you. If you are lucky you can get into this iPhone if they (owner) accidentally remove the device from their Apple ID.