E (vs. RHE) = E (vs. Ag/AgCl) + 0.059 x pH + EoAg/AgCl

This is the required conversion equation.

EoAg/AgCl = 0.1976 V at 25oC.

Your reference electrode's (RE) potential (vs Standard Hydrogen Electrode (SHE)) basically means the voltage you will see if you connect your RE (which is a half-cell) with a SHE (another half-cell). This is Eo Ag/AgCl if you use an Ag/AgCl RE. And, this voltage is +0.1976 V if the electrolyte inside your Ag/AgCl RE is saturated KCl solution. Yes, this RE potential (vs SHE) also varies with the concentration of the electrolyte inside the RE, which make sense because the concentration of the Cl- (in that electrolyte) directly influences the electrochemical reaction inside the RE (AgCl + e- → Ag + Cl-). So, first, accurately find the RE potential (vs SHE) for your electrode. There are ways to calculate that, and, you can also find it in the manufacturer's manual for this product.

After that, use your RE potential (vs SHE) to see how your data looks like in terms of the SHE. You need to be careful about that '+' in the +0.1976 V, this indicates a reduction reaction vs SHE (conventionally taken). For instance, if your targeted reaction in the cyclic voltammetry experiment is a reduction reaction, and you get some current value (which is generated by that reduction reaction) at a certain applied voltage vs Ag/AgCl, you need to add 0.1976 V with that voltage (vs Ag/AgCl-with saturated KCl inside) to set your scale vs SHE (ESHE). This is because your Ag/AgCl RE is already reduced with a 0.1976 V against the SHE.

Now, use the formula below to set your voltage axis vs RHE:

ERHE = ESHE + 0:059 * pH (of the electrolyte you used for the experiments).