To allows less secure apps in Gmail account follow the steps below
Note: Disable Two-step verification first. After that, the option to allow less secure apps will appear.
Step 1: Sign in to your Gmail account using the login credentials.
Step 2: Click on the Profile button and press the Mange Your Google Account option.
Step 3: Now, choose the Security tab and scroll down to Less Secure App Access.
Step 4: In the next wizard, click on the button to enable the less secure application access.
Step 5: At last, you have successfully enabled the less secure application access.