Strip Characters in Dial plan

[locious]

1. Brekeke Product Name and Version: SIP Server 3.9.5.8

2. Java version: openjdk 11.0.5

3. OS type and the version: Windows Server 2016

4. UA (phone), gateway or other hardware/software involved: SPOK

5. Your problem: How can I strip characters in the from header in the dial plan?

Here is the from header I'm working with: From: INPT212_1 Patient <sip:a300*r212*b1@domain.com

Basically I want to remove the "a", "r", "b" from the URI (Highlighted above in red) before deployed.

[Harold]

[Matching Patterns]
$request = ^INVITE
From = sip:.(\d+)\*.(\d+)\*.(\d+)@

[Deploy Patterns]
From/uri/user = %1%2%3