You aren't going to want to use a script for this type of Access Control. There are two places to look at. The first is the list or table configuration to identify if inline editing is turned off this may appear as something like a checkbox that read "Hide option to quick edit". Based on your comment about having previously been able to do this then its possible this has been changed. This is easy enough to check quick, if you can edit any field on the list then this is turned on and you don't need to investigate farther and need to move on to checking Access Controls.
The ability to change any specific column may be blocked at several levels within Access Controls so make sure you have write access at the table level to start. If you have write at the table then determine if there is a record level ACL in place and if so make sure you also have record level write access. After that you will need to also verify that there is not a field level Access Control that is restricting access and if so make sure you have field level write access.
To achieve what you are asking to do with a script you would instead create an access control structure as above. If you aren't familiar with how the access control hierarchy works then you should probably do a bit of study on that first so you don't unintentionally allow or restrict access when trying to implement your plan. In general the most granular Access Control always takes priority so if a field level Access Control exists then it overrides any record or table level Access Control.
For example, if a field level control allows write permission to your Opened For field, then a user will need to have write access granted by that access control rule even if they have record or table level write permissions.
