I attempted to add the journal name for my paper, but I couldn't find it even with the ISSN number. The journal can be identified by the publisher IUST.
Dear A. Kaveh Have a look at https://help.researchgate.net/hc/en-us/articles/14293139566353-Journals It might be somewhat frustrating (and even unfair) but in cases where the journal is not present in the RG database you cannot add them yourself and in rare cases new titles are added (but require patience).
Dear Colleague, to add the International Journal of Optimization in Civil Engineering to ResearchGate, first ensure you have a ResearchGate profile. Then, go to “Add new” > “Publication” and select “Article.” Fill in the article details manually, including the journal name. If the journal is not recognized, you can still add it by typing the full name and continuing. Upload the full-text PDF if allowed by the publisher. If several articles from the journal are added over time, ResearchGate may eventually index the journal automatically. Encourage fellow authors to do the same to increase visibility and recognition.