Merge multiple InfluxDB 1.8 dbs + add tag with name of each?

Hi all.

I have multiple InfluxDB 1.8 databases with same schema.

I need to merge them into a single database
& add tags with names of the original databases the data came from.

How to achieve that for all data?

~ 20 databases
total size: ~ 200Gb
No retention.

Thanks.