How to use custom ISP database in geoip?

The ISP database from MAXMIND is only suitable for USA ISP, and not correct out of USA

The ISP name is about 95% accurate in the US. Outside the US, accuracy ranges from 50% to 80%, depending on the country. The data is generally more accurate for countries with more Internet users.

I got a csv formatted isp data suitable for my region.
How can I use it?

Thank you for help!

You would need to change it to the same format as the maxmind one.

Thank you, @warkolm

But the filter seems not support csv. I saw that all the samples were binary .dat

geoip {
      database => "/etc/logstash/geoip/GeoIPASNum.dat"
      source => "src_ip"

I've found some tool for transforming csv to maxmind dat. mmutils

But my csv file contains characters out range of ascii, and then result in unreadable

"fields": {
          "isp.isp": [