Go to Resources >> Import textures >> Import mob, GUI, logo, etc (or press CTRL+SHIFT+7) >> Add/select the desired *.png file (image), then click on Workspace >> Workspace settings (or press CTRL+ALT+P) >> In General settings tab, look for Mod logo picture, select your recently imported image/logo >> Save and test
Go to Resources >> Import textures >> Import mob, GUI, logo, etc (or press CTRL+SHIFT+7) >> Add/select the desired *.png file (image), then click on Workspace >> Workspace settings (or press CTRL+ALT+P) >> In General settings tab, look for Mod logo picture, select your recently imported image/logo >> Save and test