I never used call parking and I don't have a 3cx account, so I didn't test the following.
Park a call - Blind Transfer to *00 thru *09
Pick up a call - *10 thru *19 optionally followed by extn#
https://www.3cx.com/blog/voip-howto/parked-call-desk-phone/Assuming:
SP1 is connected to 3CX
SP1 is your primary line
Use OBi Expert to make the following changes:
Service Providers -> ITSP Profile A General -> DigitMap
Add the following after the beginning (
*[01]x.S3|
Define a Programmable Key as a blind transfer
IP Phone -> Programmable Keys -> Key x
Function: Blind Transfer
Service: SP1
Park a call by pressing the program key defined above
Enter *01
Press Dial
Pick up a call
Dial *11
Optionally dial *11 followed by an extension number