1. Make sure you have an Office 365 subscription, and that your Excel version is up to date.

Excel Online, used through a web browser, is always up to date -- proceed to Step 2!
On a Mac, you'll need Excel Version 16.25 or later. Choose System menu - Help - Check for Updates.
On Windows, you'll need Version 1904 or later. In Excel, choose File - Account - Update Options - Update Now.
If you don't get Version 1904 or later, you are on the "Semi-Annual Channel" - Click here for steps to switch to the "Monthly Channel".

2. Access the "Store" - Microsoft AppSource.

In Excel Online, Excel for Mac or Windows, click the Home tab, then Office Add-ins (It is the four red squares). 
In the Office Add-ins dialog (pictured below), click the Store tab.

3. Find and insert the Analytic Solver Add-in.

In the Search box, type Analytic Solver, then press the Enter key. You'll see both "Analytic Solver" and "Analytic Solver Data Science".
First click the Add button next to Analytic Solver. Read and check the box to agree, then click Add again.

4. Find and insert the Analytic Solver Data Science Add-in.

Repeat steps 2 and 3, but this time click the Add button next to Analytic Solver Data Science. Check the box to agree, then click Add again.
You've now completed the installation process! The next step is to log in and activate your trial license.

5. Login to use Analytic Solver.

Click the Analytic Solver tab on the Ribbon. If you don't see the Task Pane on the right side, click the Model button on the Ribbon.
Click the Get Started button in the Task Pane. A Login dialog pops up. (If you don't see the button, you are already logged in.)
Enter the email address and password you use on Solver.com, and click Login.

You're Ready to Start Solving!

Choose Help - Help Center from the Ribbon to access User Guides, Example Models, our Knowledge Base, Support Live Chat, and more.
Choose License - Manage Licenses to check your license status, renew or upgrade. You can also Login and Logout via this menu.