There are many formulas! This usually means that some of them are OK in general for estimation purposes, but none of them will be especially accurate. Not easy to choose from the many formulas.
One of the most simple and popular seems to be the Wright equation,
$$\log_{10}\left(\log_{10}\left(\nu + \lambda \right)\right)=A-B\log_{10}(T),$$
where $\nu$ is the kinematic viscosity, $\lambda$ is a parameter, usually taken to be $0.7$, and $A$ and $B$ are compound-specific parameters. With knowledge of linseed oil viscosity at least one other temperature than the one you provided in your question, you could fit $A$ and $B$ parameters and apply the equation.
However, the best answer to your question is to obtain some empirical data. A 1977 paper[1] reports on linseed oil viscosity as a function of temperature, for example. They found that a different equation (not the Wright) gave a reasonable fit to the data. Specifically, they found
$$\ln(\eta) = -5.73 + \frac{2820}{T}$$
for viscosity $\eta$ in centipoises and temperature $T$ in K.
Another thing to keep in mind is that linseed oil is prone to oxidation. Oxidized linseed oil may have different properties than undergraded, "pure" linseed oil.
[1]: T. Gallagher; D. E. Kline; J. Am. Oil Chem. Soc. 1977, 54 (2), 68-70. DOI: 10.1007/BF02912392
