In SharePoint i have a infopath form.If i enter comment in textbox in Workflow History list User ID field it save as System Account. Why its happening and how to change the system account to Logged in user.
I'm assuming that you have a workflow under the list which has an infopath form to fill data.
I'm also assuming, that this workflow was made with the "system account" and that it uses an "App Step", this means that the workflow is using the system account to elevate it's permissions to do whatever the workflow needs to do that the normal user account can't do.
If that is the case, you can't change this behaviour. If it's not the case, remove the App Steps, or it could also mean that the list column became corrupted.
What you can do is create a user or text column, go into "infopath > Data > Form load" and create a rule that will pick the userName() and fill the created column. Then modify the workflow so that it records that created column as the user that filled the form in the history (While you can't change the System Account as the actual account, you can save this information elsewhere).