How to convert from %FSR to LSB (DAC)?
If \$p_\%\$ is the quantity in percent of \$FSR\$ and \$xLSB\$ is the correspondent representation in LSB:

$$ 1 LSB \rightarrow \frac{FSR}{2^n-1} $$
$$ x LSB \rightarrow \frac{p_\%}{100}\times FSR $$

$$  x LSB =  \frac{p_\%}{100} \times (2^n-1) $$

An example from SLAA013 - Understanding Data Converters from Texas Instruments:
... offset  error,  gain  error,  integral  nonlinearity  and  differential nonlinearity. Each can be expressed in LSB units or sometimes as a percentage of the FSR. For example, an error of 1/2 LSB for an 8-bit converter corresponds to 0.2% FSR...