Install wmctrl

sudo apt install wmctrl

And create a script (in this example thunderbird on the second workspace (-t 1)):

#!/bin/sh (thunderbird &)  & sleep 5 && sh -c "wmctrl -i -r `wmctrl -l | grep Thunderbird` -t 1"

To know your application name on wmctrl you can view it by taping on your terminal :

wmctrl -l

And replace it with the correct name in the script.

Be carrefull with the capital letter ("Thunderbird" not "thunderbird") !!

Other example with firefox on the 3d workspace (-t 2):

#!/bin/sh(firefox &)  & sleep 5 && sh -c "wmctrl -i -r `wmctrl -l | grep Firefox` -t 2"

Bonus :

Here is the command to execute at start-up :

sh -c "thunderbird  & sleep 5 && wmctrl -i -r `wmctrl -l | grep Thunderbird` -t 1"

Work on Debain 10 with Cinnamon. But should work for all