The commit that added support for this device says
The WG3526 is the follow-up to the 2626 and is mostly the same, with the
excaption that the mt7602 has been replaced with the mt7603. The internal wifi
setup has also changed slightly. Based on my tests, everything that worked on
the 2626 works on the 3526 and with roughly the same performance.
https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=30fbc1a4d146ae0060d02946709fd6d8cc2a2b56
So I think you need to follow the instructions for the wg2626 https://openwrt.org/toh/zbt/wg2626