This Pali-English dictionary translates atta as “oneself”:
atta : [m.] soul; oneself. || aṭṭa (nt.) 1. lawsuit; 2. watch tower; 3. a scaffold for workers. (adj.) (from aṭṭita:) grieved; afflicted.
https://www.budsas.org/ebud/dict-pe/dictpe-01-a.htm
This dictionary states
anattā (n. and predicative adj.) not a soul, without a soul. Most freq. in combn. with dukkha & anicca
http://dsalsrv02.uchicago.edu/cgi-bin/philologic/getobject.pl?c.0:1:533.pali
There seems to be no difference between atta and attā. Both can lead to anatta or anattā?