Manual:Reset
From MikroTik Wiki
RouterOS password can only be reset by reinstalling the router, or using the reset jumper in case the hardware is RouterBOARD.
If u lost the password on router board u may reset by this procedure:
1. Reset the router board. 2. Press any key when it's tell u to do that. 3. Type r
Example
MikroTik 3.0rc13 MikroTik Login:
RouterBOOT booter 2.12
RouterBoard 1000
CPU frequency: 1333 MHz
Memory size: 512 MB
Press any key within 2 seconds to enter setup.
RouterBOOT-2.12 What do you want to configure?
d - boot delay k - boot key s - serial console o - boot device r - reset configuration e - format nand g - upgrade firmware i - board info p - boot protocol t - do memory testing x - exit setup
your choice: