Unfortunately, I hadn’t read that there is no way to recover my lost password to admin panel, and I reset my router (Tenda W311R) thinking that the password will restore to default as well. What can I do now? Only do a software reinstallation? Did my password change to something random? If not, my ISP should know what password set.
Why do you think that Mikrtik’s forum is proper place to ask about problems with Tenda router?
I have just kindly asked and I ask for a help. Does it matter that my router is Tenda, since it’s powered by Mikrotik RouterOS v6.41.4? Their manual says that in the case of password lost only what I need to do is to reset the router and username/password should set to admin/admin.
Surely you call Apple customer support when you have issues with your HP laptop running Windows?
Could you only tell me if password remains untouched or changes after reset?
OK, so it’s not Tenda after all.
Default password on ROS is empty password. If that doesn’t work, it might be set by whomever you got the router from and is highly unlikely for you to get correct answer from this forum. And, if you don’t find out password, the only way getting in is netinstall device.
Does password remains untouched or changes after reset? Does the same is true for username?
If you perform factory reset, then everything gets reset to factory defaults, including usrnames and passwords.
OK, perhaps not just everything, malicious code might survive 
There’s a gotcha: it is possible to install custom defaults (after netinstalling device) and some ISPs deliver RBs to their customers configured in such way … to avoid hassles when customers manage to perform factory reset and ISPs loose administrative access causing technician visit to customer’s premises. With such defaults it’s only ISP who knows details.
How that what you said corresponds to FAQ which states:
How can I recover a lost password?
If you have forgotten the password, there is no recovery for it. You have to reinstall the router.
I’m not sure about how verbosely you want to understand reinstall in the quoted FAQ. Namely: if you do the factory reset, you’ll have to reconfigure the whole setup (again) and this part of the exercise is exactly the same as with netinstalling the unit.
BTW, Mikrotik is a Latvian company and I doubt they have many English native speakers on their payrolls (if any). I may be wrong though.
Anyhow, there have been numerous cases where wording in their documentation was … well … not precise enough and that caused some fierce discussions about what exactly their document was telling …
BTW2, I’m not holding you from netinstalling the device. If you want to, go ahead, I’m not going to try to stop you. Actually that might be a good idea, there are some device states (mainly after they’ve been hacked) from which it’s only possible to recover by netinstalling the device.