Request for help- MDS analysis

I need help with the SPSS software, hopefully someone can help me.

I need to do a MDS (Multy Dimensional Scaling) analysis, but I am having problem with analyzing it with the SPSS.
My data is a not-symmetrical similarities matrix. Is that possible to use it as input?
If not- what should I use?
Is there a particular function I should choose?

Please, any help would be blessed