A 4-week digital foot self-management program will be provided to the participants in experimental group.

The control group received routine care that are required to attend the education sessions in the diabetes clinic according to their scheduled appointments. Routine care included routine check-ups and foot care education.

A 4-week digital foot self-management program based on Bandura's Self-Efficacy model. The proposed functions include checking conditions of foot, cleaning, cutting or removing corns and calluses, trimming, clipping nails, foot exercise, dietary related to foot care, foot care logs, etc. Which was developed for older adults with diabetic foot self-management by the study team. Week 1 one-hour face-to-face training session after participant recruitment and allocation. The outline session is 30 min to introduce key topics and function in the app platform, 15 min to install the app and to demonstrate the use of the app, 15min to discuss and practice. Week 2 to week 4 following phone call once per week at the end of week and LINE messages 3 times per week.by research nurse, who will encourage and monitor participant's compliance with the program at home by using the digital platform. Participants are informed that technical phone support is available during the trial.

Foot care self-efficacy was assessed using the Foot Care Self Efficacy Scale consisted of 16 items to measure individual's competence to manage foot care. Cronbach's alpha was .72. There are 16 items on the self-made scale in this study. Scored using a five-point Likert scale: "completely disagree", "slightly disagree", "no opinion", "slightly agree" and "completely agree", with a maximum score of 80 and a minimum of 16; represented higher values indicate higher foot care self-efficacy (Chen, 2005). The reliability Cronbach's alpha values were 0.82 in this study. The scale was used at baseline and week 4 for participants in both control and experimental groups.

Diabetic foot self-care behavior was assessed using the Diabetic Foot Self-Care Behavior Scale, a 7-item questionnaire. Cronbach's alpha was .73. The scale consists of seven questions, divided into two parts. The first part was the number of days of foot care activities and the second part was the frequency of foot care activities. On a 5-point Likert scale (never, 0 days a week= 1 point; rarely, 1-2 days a week= 2 points; sometimes, 3-4 days a week= 3 points; often, 5- 6 days a week= 4 points, 7 days a week= 5 points, with a maximum score of 35 and a minimum of 7. Represented higher scores indicate good foot self-care behavior (Chin & Huang, 2013). Internal consistency Cronbach's alpha was .89 and test-retest reliability was .92 in this study. The scale was used at baseline and 4-week for participants in both control and experimental groups.