If you need to assign a password to the new WebStore users, you should do it from the web version web.selbuk.com
Clients > Multiple adjustments
Touch Activate Webstore
On the pop-up window you may assign the password for the new customers of the WebStore and then touch Transfer - Update
keep in mind: this process will apply to the customers that have an email registerd on their profile.
Also you may set a new password to an specific customer for thye WebStore. That is from Clients > View Edit > search the customer
then on the password box type the new one and save