Follow this guide to make a custom cotton swab.

You can also use dental picks with barbed tips (non-flavored).

You can use a normal cotton swab, but most are too thick and have loose cotton that can snag on the pins.

Apply a few drops of highly-concentrated isopropyl alcohol (>90%) to the cotton.

Insert your tool into the charging port.

Don't force the tool into the charging port, as you risk bending the pins.

Slide the tool back and forth along the charging port to clean it.

Wait a few minutes for the isopropyl alcohol to evaporate before plugging in your iPhone and testing it.