I've moved this from the Using the Community forum (which is the forum for issues using the forums) to the Illustarator forum so that proper help can be offered.
Which version of Illustrator are you using?
In the Edit menu you may find the Recolour Artwork command and its dialog. It could help.
So, I don’t really understand how to use the Recolor Artwork in Illustrator properly, but that doesn’t stop me from using it anyway. I do this a lot here at work when a customer doesn’t realize the difference between RGB/CMYK and Spot color.
I’m sure there are steps that are not necessary and I do hope there is a better way, but this one works for me, and since no one else has responded, I’ll share my crazy method with you, since we all know that you don’t have to show your work in PrePress, you just have to end up with the correct number of plates.
Change the color space of that artwork from RGB to CMYK.
Delete all the unused colors from your swatch menu. (This is super important)
Create two shapes off to the side on the pasteboard (I use squares but it doesn’t matter), and fill one with 100% of the Pantone Blue, Fill the other with White.
Select both, and then created a blend (Object >Blend>Make). Create two more shapes, fill one with 100% of the Pantone Red Color, Fill the other with White. Select these two and create a blend (Object > Blend > Make).
Select the Red Blend and Expand it from the Object Menu.
With all of the pieces that created selected, “Create a New Color Group” in the flyout menu of the Swatch panel. Make sure that from “Selected Artwork” and Include “Swatches for Tints” are checked.
Choose the blue Blend and Expand it, and with all the pieces that are selected, “Create a New Color Group” in the flyout menu of the Swatch panel. Make sure that from “Selected Artwork and Include “Swatches for Tints” are checked.
Your swatch menu should now have a two color groups - each containing a large number of tints of each specified Pantone color.
Delete those shapes and expanded parts off the pasteboard so you only have the artwork you need to recolor. Select all.
Click the Recolor wheel in the top bar, In the dialog box that comes up, Change the Preset from “Custom” to “Color Library” and then choose “Document Swatches” from the Library choices.
Click OK. Your artwork is now recolored.
Again - this isn’t perfect, orderly or even sane, but on deadline, it works. I've attached the file converted to color spot below.