How do I copy player data from one account to another in the same bedrock world?

This is what I was trying to ask you before the moderator deleted my response, and since I don't 50 rep (Which is stupid) couldn't answer the question. You should be able to click on the top level tag like "Inventory" in this picture and then click the button at the top of the screen, circled in red. Then find your friends new character and paste this copied tag in with the paste button\located to the right of the copy. Hopefully this saves you some time move each individual item.

Try this program instead. You can copy the whole player folder and paste it.

https://www.universalminecrafteditor.com/