In the given setup from reddit, the interface that is used to connect to "hotspot" is wlan1 (2.4Ghz) if you will be connecting to the hotspot through wlan2 (5Ghz) then just swap wlan1 to wlan2 in all the places from the given "code" in reddit
Set your last bridge port interface the one you are currently connected via laptop, as you will get a disconnect <--- via cable or via wifi? And ... where?
It will be a brief disconnect if you are connected through mac-telnet, if telnet, then it shouldn't even occur. Just put all interfaces under the same bridge ports except the one (wlan) that will be connecting to the hotspot
/interface bridge port
add bridge=bridge interface=wlan2
add bridge=bridge interface=ether1
add bridge=bridge interface=ether2
add bridge=bridge interface=ether3
add bridge=bridge interface=ether4
add bridge=bridge interface=ether5
Before applying, set the default wireless security profile wpa2 password to the public networks password (or delete the entire line if public with no authentication) <--- where?
Default security profile is used to connect to the hotspot, password is being set here (PublicNetworkPassword)
/interface wireless security-profiles
set [ find default=yes ] authentication-types=wpa2-psk mode=dynamic-keys supplicant-identity=MikroTik wpa2-pre-shared-key=PublicNetworkPassword
Here (YourPrivateNetworkPassword) is added a different password for your other network, not necessary if you want your "repeating" network to have the same password as the hotspot
/interface wireless security-profiles
add authentication-types=wpa2-psk mode=dynamic-keys name=5Ghz supplicant-identity=MikroTik wpa2-pre-shared-key=YourPrivateNetworkPassword
Set the wlan1 (2.4Ghz) SSID to the public networks and adjust the Wlan2 (5Ghz) to your liking <--- how?
2.4Ghz is set through wlan1, just change the PublicNetworkSSID to your hotspots SSID
/interface wireless
set [ find default-name=wlan1 ] band=2ghz-b/g/n channel-width=20/40mhz-XX disabled=no ssid=PublicNetworkSSID
The same goes for 5Ghz (YourPrivateNetworkSSID) if you choose to keep the same password then change security-profile from
5Ghz to
default
/interface wireless
set [ find default-name=wlan2 ] band=5ghz-a/n/ac channel-width=20/40/80mhz-XXXX disabled=no mode=ap-bridge security-profile=5Ghz ssid=YourPrivateNetworkSSID
Also, it is highly advised to set your routers password for configuration via /password in terminal, or you can create a new user through /user add <--- is it the admin password or the one of a different user?
Simple
/password will adjust the admin, press enter (leave empty) when required the current one as you probably have it empty, then repeat twice the new one.
I'm pretty sure I confused you in many more ways. best would be to copy the code from reddit to a notepad or something and edit the parts given above to your liking and copy the entire thing into the terminal or step by step from top to bottom.