@madecenik This is not currently possible. If you're interested in improvements to the way new groups are added including the possibility of introducing a button to add more repeats as you suggest, please share your thoughts on how this should work at Refinements to Repeat Group Navigation - #9 by tomsmyth.
If your data collectors will know ahead of time how many of the group they need to fill out, I highly encourage you to prompt them for that count first and automatically generate the right number of repeats. For example, if the data collector is filling out information about members of a household, they can first ask how many people live in the household. See the repeat documentation for examples on how to do that.
If you don't know the number of repeats and you want to remove the first prompt to add a group, you can remove jr:template from the XML. This is not yet available in XLSForm but hopefully will be soon. See Add New Group: Add initial group automatically - #3 by Maya for more.