how to combine if and for loop?

I'm using Arduino uno, fm transmitter and LCD, I'm trying to change the frequency every minute or more. both for and if loop works alone.

//#include <FMTX.h>
#include <Wire.h>

#include <LCD.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,2,1,0,4,5,6,7,3,POSITIVE);
float fm_freq;

void setup() {
// put your setup code here, to run once:
lcd.begin(16,2);
lcd.backlight();

// Serial.begin(9600);
// Serial.print("FM-TX Demo\r\n");
//
// fmtx_init(fm_freq, CHINA);
//...

how to combine if and for loop?