We can get the Security Token by following two steps:
Step 1: is when we change the password of our account then a confirmation sent to the registered mail with the “Security token”, just like the below screenshot:

Step 2: the way is by resetting your security token, to do that follow the simple steps:
From “Lightning Experience”: click on the user image that is located on the top right on the screen, a popup menu will display then, click on the “Settings” link. And after selecting “My Personal Information”, and then click on the “Reset My Security Token”, nowhere a “Reset Security Token” button is displaying.
[For more detail see the screenshot]

From “Salesforce Classic”: click on the username a popup menu will open and click on “My Settings” options. And after under “My Settings” section, select “Personal”, here click on “Reset My Security Token” option, nowhere displaying “Reset Security Token” button is displaying.
[For more detail see the screenshot]

Now, when we click on the “Reset Security Token”, a new Security Token will be sent to your registered E-Mail address.
[In detail see the screenshot]
