I would start by guessing that it is 1X, since no other information is available. You could try using the method given in the original paper by Bradford. https://hoffman.cm.utexas.edu/courses/bradford_assay.pdf

I use a microplate version, in which a 10 µl sample in water or a non-interfering buffer is mixed with 200 µl of 1X Bradford reagent, and read at 595 nm after 5-10 minutes. The amounts of BSA depend on the quality of the Bradford reagent, but I use either 0.5-5.5 µg or 1-11 µg to make the standard curve. I fit the absorbance vs. µg BSA data with a 2nd order polynomial, but a linear fit may work well, especially for the lower concentration range.