This is /was your computer (Acer Aspire T3-710):
At least with respect to the case,,,,
https://icecat.biz/en/p/acer/dt.b1hef.007/aspire-pcs-workstations-4713392244094-t3-710-29531013.html
And you removed the original motherboard and installed the B450M Pro motherboard.
Yes: You will need an adapter of some sort to change the original 13 pin case to motherboard connector to a 9 pin connector of some sort . Again case to motherboard with respect to the front panel connector.
I likewise did some googling and did not note any adapters that I felt would be applicable and/or safe to use. The concern being some mismatch in pins and voltage even though it all should be standardized.
You will need to take the original 13 pin plug and map out each pin with respect to pin number, function, and voltage.
Then do the same for the 9 pin connector. Pins that match are the pins that need to be connected either direct (if possible) or via some adapter as is the question/problem at hand.
Big picture (literally) is that you end up with a diagram something similar to what shown in the following link:
https://linustechtips.com/topic/1211609-motherboard-front-panel-connector/
Read the link carefully and do note the reference to the B450 motherboard as well.
The link shows an adapter that may be applicable for you.
Google "10-1 System Panel Adapter": I found the following link along with other similar links.
https://www.moddiy.com/products/Asu...tor-10-Pin-System-Panel-Connector-20-Pin.html
Do double check everything to verify that that adapter or similar ones are a match to meet the required connectivity.
Should be standard and fall right into place. However, no harm in being very sure.