When restoring Termux from a backup, how can I specify which shell Termux to use (sh or bash) and how to specify which init files this shell to use?

Question

Because the shell(s) below of Termux are throwing error continously which cannot be canceled with ctrl-c or other means - due to a vim which cannot find/read .vimrc - and since shell actions in Failsafe mode are also of no help, I am looking for a way to control from outside of Termux what Termux will do after it is launched. Regards.