Looking up values across tabs

Good morning all,
I have a requirement to do a lookup, which i believe might need a 3d function. 
I have a spreadsheet that has multiple tabs that depict different areas in various applications. And one tab that has a list of requirements. Within the various application tabs, against each line item I have the requirement it is mapped to. What I am looking to do is in the requirement tab, have one column that has list of all the applications that are mapped to this requirement. An example is as below - the last table depicts what the resultant output should look like (in the bolded column):
Application A tab:

Screen ID

Req ID

Screen Name

Comment

123

1

Test 1

 

456

1

Test 2

 


Application B tab:

Screen ID

Req ID

Screen Name

Comment

789

1

Test 3

 

ABC

2

Test 4

 


Application C tab:

Screen ID

Req ID

Screen Name

Comment

DEF

2

Test 5

 

HIJ

1

Test 6

 


Requirements Tab: (desired result)

Requirement ID

Requirement Name

Mapped Application Screen IDs

Comment

1

Req1

123,456,789,HIJ

 

2

Req2

ABC,DEF