Below is the step on how to reset password of user in Microsoft Admin Center.

Step 1 - Open your Microsoft Office 365 portal. You may use the link to Sign in to your account (microsoftonline.com)

Step 2 - Once you are logged in, on your left pane you may see the icon , click the icon then find and click the Admin icon . 

Step 3 - The Microsoft 365 Admin Center will be as per the image below.

Step 4 - On the left pane, click the User  and it will drop down the list in it. Click Active User .

Step 5 - Once you click the Active User, it will show the list of members of your domain account. 

Step 6 - By searching for the username or scrolling down the list, you may click on the username you wish to reset the password. It will show as per the image below. 

Step 7 - Click the button Reset password to start resetting the password.

Step 8 - You may choose how you want it to be reset by ticking the check box as per the image below. Then, click the button Reset password.

Step 9 - You are done. The password provides needs to be copied and given to the new user.