In general the DSCP settings are availabe on the the Activity's Advanced tab (for both client and server)
For example for HTTP client is here:
On releases prior 6.40 EA the options defined in the drop down list do not cover all the possible combination.
In that case, if you would like for example to use a custom DSCP value you will have to set in that box the TOS integer value associated to it.
integer_TOS =integer_DSCP x 4
TOS(8b)=DSCP(6B)+2B
