Best way to create a data-filling bot for a ERP

Question

Let me give you a bit of background. Currently we are using an ERP software in which we have to record some data that comes from another system. At this moment it's impossible to have access to this ERP database, so all the data recording must be done trough a very badly implemented UI. What we are trying to achieve is to automate all this data recording with a bot that cliks on the buttons and menus of the ERP user interface and writes all the information that comes from this other systems.

Do you know how can this be achieved? Or at least where can I start to look at? I'm at a complete lost at the moment.

Thanks for the help.