Elasticsearch status is in red

elasticsearch is in red status and found this log in master node.
[2020-01-14T14:25:39,232][INFO ][o.e.c.r.a.DiskThresholdMonitor] [elastic02] low disk watermark [85%] exceeded on [h_w0x3riSpS1Dh-WQANUhQ][elastic02][/var/lib/elasticsearch/nodes/0] free: 9.2gb[10.8%], replicas will not be assigned to this node
space in /var is 90%

Thanks,

I think the error message is quite clear: you are running out of disk space and can therefore not allocate new shards. You need to either add resources to the cluster or delete data to free up space.

How can i delete old data?

Is it possible to delete data in /var/lib/elasticsearch/node/0/indices?

No, delete indices using Delete index API. You should NEVER directly delete anything at the file system level directly.