I mistakenly blocked port 8291. All other methods to connect to the router except WinBox are disabled.

Is it possible to somehow access the mikrotik by knowing the administrator's login and password?

If you have a console port, use this.
If you have an USB port, you might try a WOBM.
-Chris

If you are physically connected to the router then you should be able to use L2 MAC connection through Winbox.

if all the suggestions above did not work, you can use netinstall or do a hard reset and re-configure the rb.