Welcome to the Orchid Board!
There is so much wrong with growing orchids that way, I don't know where to begin. I have no doubt there are no, or next to no, living roots inside the pots. The plants have grown roots outside the wet medium to survive.
You can repot an orchid any time it is making new roots. It is better if it is during the warm season. So, go ahead right now and repot those.
Use a pot a little larger than needed to stuff the roots in without breaking them. Make sure the pot has a large drain hole or holes. People use bark chips, sphagnum moss and LECA clay balls successfully. Oncidiums need regular and plentiful water, but they cannot tolerate wet roots without air.
If you use the Search function in the maroon menu at the top you can find many threads dealing with repotting Oncidiums.
If you are near an orchid society, they will teach you how to grow orchids where you live. And they will be very friendly.
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