I had a crash into a pool 4 days ago. Put GoPro in rice and that is doing fine. Battery for solo is a goner. Took battery tray off and gps compartment apart and air dried. After three days, tried solo with new battery. Lights came on on the battery, but solo would not turn on. Any ideas?
Since it's possible to take Solo
completely apart, that's what I'd do ASAP. If it has fallen into something
other than fresh water, and you are able to get it apart quickly, I would just rinse it in fresh or distilled water,
then start the dry-out process. Water can collect in tiny crevices of connectors, motors, etc. so after disassembly, carefully towel dry the parts and then use compressed air to blow out difficult to reach spots. I have a compressor, but canned air should work. After that, I prefer warm blowing air, rather than the rice treatment. Try a hair dryer on low heat.
A poster above had the right idea IMHO... wait 7-10 days AFTER you are
certain it's dry. BTW, there is also a small battery on the GPS board, but not easily removable.
I'm a (clumsy) boater and have had pretty good luck drying out drowned electronics over the years. Saved a cell phone after an hour in the muddy Mississippi River, used it for 3 months and drowned it in coffee (don't ask). Got it working again!
I think key points are:
- Remove power ASAP
- Disassemble completely
- Rinse (particularly if it went into saltwater)
- Towel pat dry
- Blow out leftover water particularly in/under components and connectors
- Use warm air to dry
- I suppose throwing components in rice overnight, after those prelims, can't hurt. I never use rice if I can totally disassemble, but board components in rice could help - as the last step.
- Don't reassemble and don't power-up for several days - I like the 7-10 days.

I realize that you are past some of those steps. You didn't say if the gimbal went in, but those aren't really made for disassembly so... do the steps that you can with it I suppose. Next time you fire up Solo, just try Solo alone and worry about the gimbal and GP
if Solo works.
You may also partially disassemble GoPros. Search the web for directions and check for trapped water in the GP.
Let us know the outcome...
ETA: Oil your motor bearings after you've dried the motors. Search this forum for proper oil - not WD-40, etc.