Regex tags in Telegraf

I have my snmp walk returning data in a specific format. I’ll need to take a part of the data out and I don’t know how to specify the pattern for regex.
The data is like
“0.01 mW (-23.77 dBm)”
I’ll need to take out -23.77
The values 0.01 and -23.77 keeps on changing
Please help me with it

For building regex, I really like the regex101 site:

You can dump a few lines of example data in the test strings and then work to build a working regular expression. Something like \((.+) dBm\) may work to grab the value of dBm each time.

Thanks! That helped:)