In any event, if you get notice that you cannot enter a page because you are already logged in, then this is likely an issue with these login cookies. The easy way to avoid this is to log out when done with a course session before closing the browser or before just leaving your browser open to move on to other computer projects.
After you delete your cookies, then you can login and then logout and that should put you back to normal.
There are two ways to remove cookies from your browser. One is more of a shotgun, deleting all cookies from all sites in the browser; the other method deletes cookies from just a specific website, leaving others undisturbed.
Top left menu Chrome / Clear Browsing Data... / check Cookies and other site data / press Clear Data
Surgical Delete in Chrome
(1) Go to website of interest and right click a page and choose Inspect.
(2) In the top menu bar choose Application.
(3) On the left, expand Cookies menu and highlight website.
(4) Right click the highlighted website and choose Clear.
Firefox Shotgun
Top menu History / Clear Recent History... / check Cookies / press OK
Surgical Delete in Firefox (v76 May 10, 2020)
(1) Go to website of interest and right click a page and choose Inspect Element.
(2) In the top menu bar choose Storage.
(3) On the left, expand Cookies menu and highlight website.
(4) Right click the highlighted website and choose Delete All.
Safari Shotgun
Top left menu Safari / Clear History... / select time frame / press Clear History
Surgical Delete in Safari (v13, May 10, 2020)
(1) Go to website of interest and right click a page and choose Inspect Element.
(2) In the top menu bar choose Storage.
(3) On the left, expand Cookies menu click to highlight website.
(4) On the right select any one cookie, then Cmd+A or Ctrl+A to select all, then right click and choose Delete.
Edge Shotgun
Top right 3-dot menu / History / top right link Clear history / check Cookies and saved website data / press Clear
Surgical Delete in MS Edge (Win10 v1903, May 10, 2020)
(1) Go to website of interest and right click a page and choose Inspect Element.
(2) In the top menu bar choose Storage.
(3) On the left, expand Cookies menu click to highlight web page in view.
(4) On the right select any one cookie, then right click and choose Delete.All Cookies.