You need to remove the bearings from the reel and drop into a jar containing petrol. Agitate the bearings and then use the end of a pencil through the middle to remove and spin them. Do this a couple of times to make sure they are really clean.
Dry the bearings on a piece of kitchen roll. Leave a few minutes to let the petrol evaporate, then drop into another jar containing suitable oil. Agitate again to get the air out of the bearings. Leave for a few minutes then remove onto kitchen roll to remove the excess oil, then pop them back into the reel.