When working frequently in BO Testtool (you can use transaction BOBT to start it) you have to enter the BO name.
First tip: You can enter e.g. *tor and select the BO then, that´s typically faster.
Or (second tip) : There is a user parameter /BOBF/CONF_UI_BO where you can define a default value for your favourite BO. e.g. /SCMTMS/TOR 🙂
When doing so, this BO is already selected when entering the BO Testtool.