It's in one of the service manual revisions but I couldn't find it in the current one.
See here
https://www.eevblog.com/forum/testgear/the-siglent-sdg2042x-thread/msg1243552/#msg1243552Connect 10MHz from your GPSDO to the counter input, set the AWG to counter mode and make sure it works. It's probably best if the AWG has been left on to warm up for at least 10 minutes.
Then Utility=>System=>page 2=>System Info=>123654=>Time Base Calibration.
Then you can alter the DAC code to tune the frequency.
There's a frequency display on that screen but it's a bit coarse unless you are really far out.
Then Accept and back into counter mode to check. Rinse and repeat until you get it as close as you can. You could also check the AWG output with a scope and GPSDO or a counter with an external reference.
There's also an Auto Set when you get to the screen with the DAC code. I tried it and it didn't seem to do much. I altered the DAC code.
When I bought my SDG2000X a few months back it was within about 0.4 ppm, which is well within the maker's spec. After calibrating the timebase it's less than 0.01ppm. It will be interesting to see how long it stays there.
0.4ppm is pretty good and enough for just about anything I want to use it for with its internal clock. Being able to adjust it to less is gratifying.