Hello widze,
seems that you will need a pin spanner.
Please read on here
https://www.stridaforum.com/t/photos-of-stridas-in-hong-kong/23/1]
and here
[url]http://www.stridaforum.com/forum/viewtopic.php?f=4&t=3429&st=0&sk=t&sd=a#p7175
Anyway I’d suggest you buy a new freewheel, supposably are the teeth also worn out.
http://www.strida.tv/lang-en/spare-parts/93-roue-libre-alu.html