Did you create any backup before installing the plugin? If so, we recommend you apply it to revert the update. If you didn't, we recommend you look into uninstalling/removing the plugin for now from your admin panel.
Where did you download the plugin from? Was it from this location?
If so, please keep in mind it is not compatible with 1.7. However, you should be able to download a compatible version here: https://github.com/Kendysond/Paystack-gateway-for-Prestashop-1.7
However, please keep in mind that we're unable to offer application-specific support, so if you find any issue regarding a specific plugin, we recommend you try to contact with the plugin author or with the PrestaShop community.