[glend (Glen)]

You can buy cleaning swabs online from most camera stores, or on eBay.
The actual steps in the process depend on what type camera you have, which you do not mention. The swabs can be used in most cases.
If you have a DSLR it's pretty much a reach down process, but in dedicated astro cameras, like ZWOs, you may have to unscrew the front ring section which normally opens up the sensor compartment. Cooled cameras usually have dessicant material to stop condensation, if your getting condensation in a cooled camera, after cleaning, make sure you put new dessicant in place because the old one might be saturated. Some dessicant can be dried out, some can't.