Currently the theme ( Evolve Plus 2.6.6 ) uses the site title which is found in Settings > General as the logo’s alt
If you want to make changes.
Depending on which header you are using, the files are located in evolve-plus/templates/ folder
You will have to copy it to your child theme, maintaining the folder and file structure so that it overrides the file in the parent theme.
You can do your edit in the newly copied file.
For every theme update you will need to compare your child theme file with parent theme file for any updates that has to be included.
If you require assistance in this customization, you can contact us for this service via https://theme4press.com/theme-customization-service/