Provided you first have properly calibrate each of your pedals in Eclipse, you have to understand that controlling the SEND of two algorithms is not necessary *if* the routing is SERIES. Other routings may benefit from this, though.
SEND is assigned to EXT1 by default, which in turn is assigned to PEDAL 1. This works for all presets with a SEND, in any routing configuration. If you need to change SEND of the second algorithm to a different pedal, you'll have to patch it to another EXT, which in turn should be assigned to Pedal 2.
You may leave the default SEND > EXT 1 > Ped.1 patching and create an EXT 2 > Ped.2 one; then assign the algorithm SEND in THAT very preset to EXT 2. This will only work for THAT preset (once stored), so you'll need to repeat this for any other preset you want to configure like this.
The User Manual has a very detailed section on patching controllers to Externals and parameters. It's very adviceable you read it to get the best out of your Eclipse.
all the best