Not Able to Edit the edit page in Specify information that is required for proceeding to handoff in the Lead section

Hi Team,

We are trying to add a new field and as well as make few fields mandatory in one of the edit page [Specify information that is required for proceeding to handoff] in the Lead section when we move from the handoff to sales to awaiting sales stage. [Specify information that is required for proceeding to handoff.png]

The edit page is added in the OOTB process [Handoff to sales 7.8.0 (Lead Finance)] and when we try to open the page designer “Translation result page” it open the source code page instead of the edit page [designer]. 

IS there way were we can open the “Translation result page” edit page, so that we can make the opportunity owner mandatory and add additional field or can you tell us how we can add a source code for making the field mandatory and add another field in the source code.