Option 1 — From the web (Send to Kindle)

1. Go to amazon.com/sendtokindle
2. Log in with your account.
3. Upload the .epub file.

Amazon automatically converts the Kindle format (internally AZW/KFX).

Option 2 — From PC (old versions)

1. Install via CLI for Windows: winget install -e --id Amazon.Kindle --version 1.30.59056
2. Convert to AZW3
3. Copy the .azw3 file to the correct folder. Typical path in Windows: C:\Users\USER\Documents\My Kindle Content