Multiple SPF records are not recommended and will cause authorization problems. Instead, update the existing record.
You can update your domain’s existing SPF record to authorize a new or additional mail server. For example, if you set up an outbound email gateway, your SPF record will include the G Suite server address and the outbound gateway SMTP server address.
To add a mail server to an existing SPF record, enter the server's IP address before the ~all argument using the format ip4:address or ip6:address. For example:
v=spf1 ip4:172.16.254.1 include:_spf.google.com ~all
To add a mail server’s domain, use additional include statements for each domain. For example:
v=spf1 include:serverdomain.com include:_spf.google.com ~all