Query VPC flow logs in Cloudwatch insights

There are two ways to do it, you can use the like clause on the filter like in the following example:

fields @timestamp, srcAddr
| sort @timestamp desc
| limit 20
| filter srcAddr like "10.25."

Second option is to use one of the ip functions to check to see if the ip address is in the subnet and in your case the subnet you need is 10.25.0.0/16

fields @timestamp, srcAddr
| sort @timestamp desc
| limit 20
| filter isIpv4InSubnet(srcAddr,"10.25.0.0/16")

Addtionally, here is a query that returns total bytes directed at the range of destination IPs in your range:

stats sum(bytes)
| sort @timestamp desc
| filter isIpv4InSubnet(dstAddr,"10.25.0.0/16")