Your can easily manage the A records of your domain with the help of the Zone Editor section. Just log in to your cPanel and find Domains → Zone Editor:

To create an A record, click on the button + A RECORD:

Enter the domain or subdomain name on the Name field and the IPv4 address on the Address field, then click on ADD AN A RECORD:

On the Zone Editor section you can also manage your records using the following buttons:

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Edit an A record
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Permenently delete an A record
NOTE
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Any DNS Record changes trigger propagation, which can last up to 24 hours to complete