Hello All
Is it possible to add some custom signals into the “Wait for Digital Input”? Can anybody help me? Thanks
What is a custom signal to you? 
If you’re talking about variables, you just use the last option. It’ll allow you to do something like “Wait for VarX = True”.
If you’re talking about MODBUS, PROFINET etc signals, they will appear in the Input tab if you rename the General Purpose register in the Installation → IO Setup.
Like EFN said, if you set up any fieldbus I/O or rename standard I/O under the installation tabs, those will show up at the bottom of the list you show here.