How to change the sentence into simple present tense?

Present simple sentences have one verb that is the present tense.

To change a past simple sentence into present simple you just have to change the verb into its present form. For example:

The dogs chased the cat. -- The verb chased is in the past form

The dogs chase the cat. -- The verb chase is in the present form.

Both these sentences have a plural subject (dogs).

When the subject is singular the verb form for present simple is verb + -s

The boy walked to school. -- The verb walked is in the past form

The boy walks to school. -- The verb walks is in the present singular form.