blocked passenger rear seat belt buckle

Hi All

I have 2015 Audi a4 2.0 tdi se Tecknik 163 

My daughter's managed to block her seat belt buckle with what I think is nylon string from her hood on her coat ( maybe with something on the end.)

Problem is the male seat belt won't insert and I've tried to remove the string but failed.

I have an extended warranty until arch 2016, but obviously doesn't cover this.

I've watched some youtube videos which show how to open up the mechanism to remove the blockage.

What I really like to know, is, is it relatively easy process to remove the seat belt buckle from the rear seat, without removing the seat?

If not what would my options be? I'm sure Audi dealership will charge an arm and leg, especially if they have to replace the buckle.

If it's need replacing. Could someone suggest where to buy the buckle and the cheapest route.

Many thanks