Merging more columns into one

Hello, i`m new here and have no tangency with IT, so all the help is welcome.

 

Issue #1

I have 2 tables :

1st with clients Name, Surname ; ( called Clients )

2nd with the followin columns : Project Number, Clients etc. ( called Registre )

 

I have the situation where a project number has more then 1 client. How can i view in the same box in Registre table all the clients from the Clients table ?

Example :

Project number          Clients

                                   A

    6                             B

                                   C

 

    7                             D

A, B and C should be in the same box ( project number 6 ), while D is already in a different box which correspondes to project number 7. 

 

Issue #2

I have 2 columns; one with a number ( contract number ) and one with a date ( contract date ).

I want to merge those 2 into 1 column to show for ex. 1/12.02.2020 ( 1 - contract number ; 12.02.2020 - date )

Also how can i change the date format ? i want it to be dd/mm/yy

 

Thank you !