Hi, to have Hooper as the ultimate Last Name at Birth (LNAB) you should set the merge so that it merges Hooper Pottle-1 into Hooper-209, which basically means you initiate the merge from the Hooper Pottle profile.
I also like to include as much detail as possible as to why I think these two profiles are the same person, including why I think Hooper is the correct LNAB. Eg. Something like 'the sources on the Hooper profile indicate the name should be Hooper'.