You have to sign the csr now so that you get a new trusted certificate from comodo. Comodo should to the reiussue of the certificate for free. So the step sre now:
1) Login to your comodo account and request a reissue of the ssl cert base on the csr that is shown in the ispconfig interface.
2) You will get a new ssl certificate from comodo then, copy the ontnets of this new certificate into the certificate field in ispconfig and the content of the ssl intermediate cert into the ssl bundle field. Then select save certificate as action and click on save.