Short Answer: With great difficulty ... easier said, than done ...
Certainly NOT for the 'faint hearted' ...
An original comment in 'FamilySearch':
"Merging is a complex process in which you decide if two people are the same person. If they are, you choose which information should be kept. Please take the time necessary to carefully review each possible duplicate."
Here are some "Knowledge Article" in 'FamilySearch':
How do I decide if two records in Family Tree are about the same person?
How do I merge possible duplicates in Family Tree?
Some advice ...
Start SMALL (easy, simple, ones) ...
Take your time ...
Go slow ...
DO NOT rush ...
Do your 'due diligence'; BEFORE, you attempt the "Merge"/"Combine".
Examine; &, check out, everything recorded against, BOTH, individuals/person.
Such, is to ENSURE (ie. make certain), in fact, they ARE the SAME person; before, attempting the "Merge"/"Combine".
IF, you are NOT 100% certain (ie. "Confident"); THEN, please DO NOT attempt the "Merge"/"Combine" - seek help/advice.
I hope this helps,
I would like to offer a suggestion to the programmers.
When viewing the details of 2 possible merge records in the linker, the items to be compared should line up with each other.
They do at the top of the page, but as the page progresses they drift apart.
Ultimately, the parents end up on different pages if one of the merge records has a number of children.
Welcome to the "Community.FamilySearch" Forum.
I am just another 'lowly' User/Patron ...
Great suggested enhancement.
As, your post, is actually a suggested enhancement ...
Can I humbly suggest that, you should consider REPOSTING this post of yours, as a 'standalone' suggested enhancement, in this Forum, in the "Ideas" (ie. 'Feedback') Section, under the "Topic" of either, "Family Tree"; or, "General User Interface".
The reason that I make this suggestion is that this "Q and A" Section is more suited to 'Questions' from Users/Patrons relating to Help/Assistance.
As such ...
Here are the direct links to the aforementioned "Topics" in the "Ideas" Section:
'Topic' = "Family Tree"
Home > Ideas > Family Tree
'Topic' = "General User Interface"
Home > Ideas > General User Interface
Again, great suggested enhancement.
I hope this helps.