Configuring a wireless router as access point?

Here is my situation: one of my computers cannot backup to to a mapped network drive despite being able to transfer to and from the mapped drive.

my network is currently: router > 24 port gigabit switch > 4 computers / NAS / wireless router > 1 computer

The 4 win10 computers that are hardwired to the gigabit switch are able to make backups to my network share on my NAS no problem but my 1 win10 computer that is behind the wireless router cannot. (tried win10 backup, win7 legacy backup and veeam and they can all connect to and see the share but fail the backup)

Why am I using a wireless router beyond the main router? I have a large building and even with 3 supplied high power access points from our ISP there is still 1 dead spot in the building and it just happens to be where one of my main PC's is, I would run an ethernet cable here but would have to rip out a few walls and trying to avoid that.

Originally I just connected the wireless router to solve the dead spot but now because of what I assume are subnet problems with the backup I would like to configure it to just be a passthrough access point.

My question is is this the best way to go or is there some other way that I can configure my wireless router to avoid conflicts?

Sorry about the long-winded post but wanted to be thorough.