The datasheet is in Chinese which I don't speak / read but it appears to be a remote control sender with keyboard matrix inputs (rather than just an "IR chip").
Figure 1. The keyboard matrix (simple version) from the datasheet.
The matrix scanner will typically pull each of the pins high (or low, depending on the logic) in turn while monitoring all of the other pins as inputs which are weakly pulled low. If one of the input pins is pulled high then a key press is registered. The thing to note here is that every pin is both an output and an input and it's not just a matter of connecting an input to ground or +3 V.
To do what you want you could try using a CMOS analog switch such as the CD4016.
Figure 2. A CD4016 CMOS quad analog switch. Image source: Components 101.
You will only require 1/4 of the chip. Drive the chosen switch's control input from your microcontroller and connect the keyboard matrix scanner lines to the chosen switch's IN and OUT pins.
Double-check the chosen 4016 for minimum operating voltage but as far as I can remember they work at < 3 V.