Just get the charger port replaced. It's really hard (well pretty much impossible) to clean the inside of a lightning port for liquid damage.
In some cases it may be more than just the charging port damaged so I recommend getting the phone opened up and inspected for liquid damage.
Replacing the charging port is fairly cheap so I'll link a guide on how to do it and where to buy the part:
iPhone 6s Lightning Connector Assembly Replacement
Where to get the part:
iPhone 6s Lightning Connector and Headphone Jack
Image of a clean charging port:
Image of a good charging connection: