Evaluating the quality of evidence for outcomes reported in systematic reviews involves consideration of within-study risk of bias (methodological quality), directness of evidence, heterogeneity, precision of effect estimates and risk of publication bias.
Choosing an appraisal tool can be overwhelming, particularly if your review will include multiple study designs. In these cases, you can use a different existing tool for each methodology, or create your own tool that will sufficiently assess multiple methodologies. The most important aspect of this step is to ensure some kind of evaluation of the trustworthiness of the evidence is conducted, so that you can give more weight in your synthesis to the higher quality studies.
If you're using Covidence for managing your systematic review, you have the option of conducting your quality assessment within the Data Extraction section of Covidence. You can either use the default template (Cochrane's Risk of Bias tool) or choose to start from scratch and build your own.