How many extensions are you trying to assign applications to?
You can chose any given instance of a file with the extension you want to assign, open its Properties, General tab, and then look at the Opens with entry. If you want a different program to open all files with that extension, then activate the Change button and go through the process of picking a different application. After you've done so all files with that extension will open with that program until and unless you were to go through this process again, or install another program that handles this file and allow it to be set up as the default handler during the install.
Brian - Windows 10, 64-Bit, Version 21H1, Build 19043
Nothing in all the world is more dangerous than sincere ignorance and conscientious stupidity.
~Martin Luther King, Jr.