Very good question.
First you need to ensure your server supports TLS2.0. You can test it here https://www.ssllabs.com/ssltest You are aiming for an A but specifically you want to see that TLS 1.2 is enabled. So in your results, scroll down to the Configuration section and look for TLS 1.2 set to Yes. If TLS 1.0 and TLS 1.1 are also enabled contact your hosting company and ask when they plan to disable. If not disabled you might have issues passing PCI Scans.
Second, since authorize.net has disabled TLS 1.0 and TLS 1.1 on their sandbox ( https://community.developer.authorize.net/t5/The-Authorize-Net-Developer-Blog/TLS-1-1-and-1-0-Disabled-in-Sandbox-on-April-30-2017-Updated/ba-p/57726) you can test your specific module by changing to test mode and verifying it still works. If it does not work then I suggest you first update it to the latest version for your specific osCommerce version and retest. If you still have problems then post the details here: osCommerce Version, Authorize.net AIM version, error details.