Make it past tense...

Which word/s should i change…

“The drug, which act as a co-surfactant, may affect the geometry of polyoxyethylene chains of the surfactants at the interface, which may compensate for the loss of surfactants at the interface between oil and water dilution and thus extends the single-phase area”

To correct your original (present tense) sentence, you must change the underlined words:

The drug, which act as a co-surfactant, may affect the geometry of polyoxyethylene chains of the surfactants at the interface, which may compensate for the loss of surfactants at the interface between oil and water dilution and thus extends the single-phase area.

Then, to change the corrected sentence to past tense, you must change the underlined words:

The drug, which act as a co-surfactant, may affect the geometry of polyoxyethylene chains of the surfactants at the interface, which may compensate for the loss of surfactants at the interface between oil and water dilution and thus extends the single-phase area.

So…i should change the sentence like this?

“The drug, which acted as a co-surfactant, could affected the geometry of polyoxyethylene chains of the surfactants at the interface, which could compensated for the loss of surfactants at the interface between oil and water dilution and thus extended the single-phase area”

is it correct?

TQ

For past tense? No. I have underlined the problems:

The drug, which acted as a co-surfactant, could affected the geometry of polyoxyethylene chains of the surfactants at the interface, which could compensated for the loss of surfactants at the interface between oil and water dilution and thus extended the single-phase area.

What is the past form of ‘may affect/compensate’? It is certainly not ‘could + -ed’.