There´s no big deal around that. I simply followed the explanations given by carll as he described above.
The main points are: You need to be locally connected via HDMI and of course with a local keyboard.
Once you do that, you can type in login. You will not be asked for any password or so.
If you want to see the file structure, use the ls command. It will show the file structures.
You should see amongst others the mnt directory. If you enter cd mnt you will get into that directory.
Another ls shows the boot directory. With cd boot, followed by another ls you will see finally see the config.txt file. Entering vi config.txt opens the possibility to edit the file.
My biggest problem was the keyboard I had, because it had a german layout and I had to figure out where some characters are located (e.g. the hyphen).
Aside of that I followed the description of carll:
"When you are ready… These are the settings I have used. this means at 35c the fan will run at 175 until temp drops 5c. I have played with this a lot over the last few days, this I found keeps my pi5 around 35c all the time with very little to no fan noise
dtparam=fan_temp0=35000
dtparam=fan_temp0_hyst=5000
dtparam=fan_temp0_speed=175"