There is a way how the supplier user can take over the task from other person (which is not in because of vacation...) from they company 

see video for supplier 

https://web.microsoftstream.com/video/85338280-d0d1-4757-8f48-54a50709ae2d

For internal users looks the functionality same but :

Under "My Team Tasks" you can shift or assign to other internal user the SP/RP . 

1. choose the correct module if you have a lot 

2. under "Action" on the right side you will see two possibilities : 

    a) Assign to Me - if you want to take over 

    b) 3.Re-Assign - if you want to assign this SR/RP to other person but please be aware that the list of person which you will see in LOV will be "per same role" = so you are CQA so only CQA will pop up or if you are OB Expert only OB Experts will pop up