There seems to be some confusion based on the comments under the question. The term keyboard in this case is a synthesizer, that means an instrument with lots of sounds, often several hundreds of sounds and lots of different styles for the rhythm box.
On such a keyboard the "one finger chords" is a standard option. You start the drum machine and then you press a key with one finger on the left side of the instrument and the chord is played. Like press C and you get a C major chord played in the style you have chosen.
Now the question is about whether the chord should be continued the whole bar. Yes, the normal thing is that the chord is continued until a new chord is indicated. You don't need to keep pressing the key, the chord will continue until a new key (for the next chord) is pressed.
It is called "one finger chords", but as soon as you want other types of chords you need to press more than one key, like C7 is C and B pressed at the same time. But as long as you stick to plain major chords you only need to use one finger.