0) Read all instructions and undertsand how it works.
1) use winbox
2) understand how it work
3) have one pc with ethernet port
4) Update both ap at same version (I suggest 6.47.9)
5) on first ap do on terminal:
and save inside the pc the generated config file (drag&drop)
6) turn off 1st ap for safety...
7) power on the 2nd and connect to it (1st time by wireless? depend how is configured at the moment) on winbox USING MAC ADDRESS
8) If all works, go inside "files" and delete all that is deletable
9) Go to system / reset configuration and check "no default configuration" and "do not backup" and then "Reset Configuration"
10) when done open the 1stap.rsc with notepad or similar, copy all on clipboard
11) Open with winbox the 2nd ap, open terminal and select "paste" from the right click of the mouse
12) Now you have two identical AP with same parameters
13) Go to IP \ address and change the IP with another free IP (usually the next), if there are not any IP, probably DHCP client is used.
14) Go to system / identity and change the name
15) go to on wireless, wlan1, on Wireless section click on "advanced mode" button and change radio-name (not wlan1 interface name)
16) Go on wlan2 and do the same
17) At this point power on old ap, go to other side of ethernet and connect the new ap, it have same parameters.
I'm Italian, not English. Sorry for my imperfect grammar.