Get a new chain and cassette. Locally everyone pretty much puts on a new cassette when the chain becomes worn, otherwise 99% of the time you’ll end out with an automatic transmission. if it skips after a new chain you need to replace the cassette. To avoid that possibility we just automatically replace both. This might be a part of the local bike culture, don’t know what ther rest of the world does as standard pratice.All good, get that chain in some WD40 stat... Though.