How to set fastboot/recovery mode on Gemini PDA for increasing root LVM volume size?

While updating SailfishOS to version I had a problem with Gemini PDA due to low disk space. I uninstalled everything I could and the update went through. I would like to increase the size of the root LVM volume size, but I could not find a tutorial for the Gemini PDA. Does anyone have experience with this?

LVM is the same on every Linux device, so these tutorial apply for the Gemini, too.

Also, if you have /dev/disk/by-partlabel/system_a and /dev/disk/by-partlabel/system_b you could probably use the unused space from one of them, though since you’re on a difrent device maybe check the content first to find out which of the 2 is used by SFOS. Use the space from a u... | SailfishOS community wiki

Thanks for the tip, but my device has only /dev/disk/by-partlabel/system so I can’t use that.
According to the instructions olf / SailfishX on Xperias · GitLab, the device must be put into recovery mode, but the recovery mode on the Gemini PDA is obviously different from the Xperia’s, the command fastboot boot sailfishos_recovery.img will not find the device.

I tried to set the recovery mode according to the Planetcom instructions - when turning on the device, hold down the “Esc” button - the recovery menu will appear, but fastboot does not recognize this state.
Then I tried Jolla’s instructions - pressed the “Volume up” button and connected the data cable. This doesn’t work either - the device goes into “charging” mode, not into “fastboot” mode.
How is it possible to get Gemini with Salfish OS into fastboot/recovery mode?

I wonder if it’s possible to boot into e.g. debian and do the partition dance from there maybe?